U.S. patent application number 14/427230 was filed with the patent office on 2015-08-27 for gravity-based foundation system for the installation of offshore wind turbines and method for the installation of an offshore wind turbine foundation system.
The applicant listed for this patent is TECNICA Y PROYECTOS, S. A.. Invention is credited to Miguel Angel Cabrerizo Morales, Jose Maria Garcia-Valdecasas Bernal, Javier Ivars Salom, Rafael Molina Sanchez.
Application Number | 20150240442 14/427230 |
Document ID | / |
Family ID | 49305011 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150240442 |
Kind Code |
A1 |
Garcia-Valdecasas Bernal; Jose
Maria ; et al. |
August 27, 2015 |
Gravity-Based Foundation System for the Installation of Offshore
Wind Turbines and Method for the Installation of an Offshore Wind
Turbine Foundation System
Abstract
The present invention relates to a gravity-based foundation
system for offshore wind turbine installation which enables the
transport, anchoring and subsequent refloating of the
structure-wind turbine assembly once anchored, giving great
versatility to the solution with regard to the uncertainties
associated with the installation and terrain response in the short
and long term, as well as the method for installing the preceding
gravity-based foundation system.
Inventors: |
Garcia-Valdecasas Bernal; Jose
Maria; (Paterna (Valencia), ES) ; Molina Sanchez;
Rafael; (Paterna (Valencia), ES) ; Cabrerizo Morales;
Miguel Angel; (Paterna (Valencia), ES) ; Ivars Salom;
Javier; (Paterna (Valencia), ES) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TECNICA Y PROYECTOS, S. A. |
Paterna (Valencia) |
|
ES |
|
|
Family ID: |
49305011 |
Appl. No.: |
14/427230 |
Filed: |
May 28, 2013 |
PCT Filed: |
May 28, 2013 |
PCT NO: |
PCT/ES2013/070339 |
371 Date: |
March 10, 2015 |
Current U.S.
Class: |
405/208 |
Current CPC
Class: |
E02D 23/02 20130101;
E02D 27/10 20130101; E02B 2017/0069 20130101; E02D 27/52 20130101;
E02B 2017/0065 20130101; E02B 2017/0091 20130101; E02D 27/425
20130101; E02D 27/50 20130101; E02D 27/22 20130101 |
International
Class: |
E02D 27/42 20060101
E02D027/42; E02D 27/52 20060101 E02D027/52; E02D 27/50 20060101
E02D027/50; E02D 27/10 20060101 E02D027/10; E02D 27/22 20060101
E02D027/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 3, 2012 |
ES |
P201200994 |
Claims
1. Gravity-based foundation system for offshore wind turbine
installation that comprises: three floating reinforced concrete
foundations built with self-floating concrete caissons, equipped
with valves for filling them with water and emptying the water out
enabling their ballasting and anchoring at their final location, a
metal structure which connects the floating concrete bases by means
of a connecting element to the wind turbine tower, and a metal
element which connects the floating concrete bases to the wind
turbine, metal element on which a docking area is installed, a
maintenance platform and access stairs.
2. The system of claim 1 wherein the metal structure is tripod
shaped.
3. The system of claim 1 wherein the metal structure is lattice
shaped.
4. The system of claim 1, wherein the attachment of the metal
structure to the three floating concrete bases is performed by
means of mixed connecting nodes, one for each floating concrete
base, each of which comprises a concrete core and a prestressing
system integrated therein.
5. The system of claim 4 wherein the metal structure comprises
three inclined diagonal rods whose ends which connect to each mixed
connecting node are conical frustum-shaped.
6. The system of claim 5 wherein the mixed connecting node further
comprises a sheet metal coating externally coating the concrete
core.
7. The system of claim 6 wherein the mixed connecting core
receives, via the metal coating the inclined diagonal rod, some
first auxiliary rods joining together two adjacent mixed connecting
nodes of each floating concrete base and a second auxiliary rod
joining each mixed connecting node to the connecting element.
8. The system of claim 7 wherein the metal coating of the mixed
connecting node has a polyhedral-like geometric shape with an upper
prismatic-trapezoidal-shaped area wherein one of their sides, the
one that receives an inclined diagonal rod, is in turn inclined and
perpendicular to the inclined diagonal rod, and a lower irregular
prismatic-hexagonal-shaped area, wherein two of its vertical sides,
which receive some first auxiliary rods linking together two
adjacent mixed connecting nodes of each floating concrete base, are
perpendicular to said first auxiliary rods, wherein the sides, at
which the inclined diagonal rod and the first auxiliary bars join,
are made of sheet steel.
9. The system of claim 8 wherein the lower irregular
prismatic-hexagonal-shaped area of the mixed connecting node
comprises a vertical side which is situated between the two
vertical sides receiving the first auxiliary rods, wherein said
vertical side receives the second auxiliary rod which joins the
mixed connecting node to the connecting element.
10. The system of claim 7 wherein the metal coating of the mixed
connecting node has a tubular-like geometrical shape and the
concrete core is situated in its interior.
11. The system of claim 7 wherein the mixed connecting node further
comprises active anchors for transmitting forces, while the
floating concrete base comprises passive anchors situated therein,
either directly on an upper closing slab or on rigidity partitions
arranged under the mixed connecting node.
12. The system of claim 11 wherein active anchors are placed in the
concrete core, comprising: transfer sheets of the four rods which
penetrate the mixed connecting node, wherein two of them, the
inclined diagonal rod and the second auxiliary bar are joined
together by welding at the point of intersection of the axes of all
the rods, transfer and connecting sheets joining the first
auxiliary rods together, and additionally, the prestressing system
is also located inside the mixed connecting node.
13. The system of claim 1 wherein each of the three floating
concrete bases comprises a lower slab which is in contact with the
terrain once the system has been submerged, an upper slab, a
perimeter wall and interior walls or partitions that define a first
group of interconnected cells.
14. The system of claim 13 wherein the floating concrete
foundations comprise a second group of cells not involved in
buoyancy for access from the upper slab to the contact surface
between the lower slab and the terrain.
15. The system of claim 13 wherein it further comprises a control
system which in turn comprises a sensing subsystem, an operational
control subsystem and decision-making subsystem wherein the
operational control subsystem enables the coordination between the
sensing subsystems and the decision-making support subsystem.
16. The system of claim 15 wherein the sensing subsystem comprises
at least one of the following: a filling level sensor for the
filling of the first group of cells to measure their ballasting
level, inertial acceleration sensors, doppler acoustic sensors for
measuring currents in the vicinity of the structure and the
distance to the seabed, a gyro for monitoring the roll and pitch of
each of the floating concrete bases, relative and absolute
positioning sensors, pressure sensors for the estimation of actions
resulting from the interaction between the ocean flow and the
system, deformation sensors for the evaluation of the number and
magnitude of stress load cycles of the system through its
interaction with the ocean flow and/or cyclic stresses transmitted
by the wind turbine.
17. The system of claim 16 wherein the decision-making support
subsystem comprises a logical device which is a first-level
instrumental alarm to generate warnings to prevent exceeding the
thresholds registered by the sensing subsystem, and a second-level
prediction device based on a climate prediction system and on the
instrumental historical records obtained by the different sensors,
performing a real-time control by the operational control subsystem
and may be displayed on a display device; an operational control
subsystem acting on the control actuators that perform the opening
and/or closing of the valves for water filling and emptying and on
a system of anchors and winches, to fix the position of the
foundation system.
18. Method for the installation of an offshore wind turbine
foundation system comprising: three floating reinforced concrete
foundations built with self-floating concrete caissons, equipped
with valves for filling them with water and emptying the water out
enabling their ballasting and anchoring at their final location, a
metal structure which connects the floating concrete bases by means
of a connecting element to the wind turbine tower, and a metal
element which connects the floating concrete bases to the wind
turbine, metal element on which a docking area is installed, a
maintenance platform and access stairs, wherein the method
comprises the following stages: a first transport stage wherein the
foundation system is towed from a collecting and/or assembly dock
to the final location by using tug boats where the floating
concrete bases are anchored, a second anchoring stage wherein the
foundation system is anchored until making contact with the seabed
modifying the overall buoyancy by the controlled ballasting of some
groups of cells in the floating concrete foundations with the
operation of valves located in said bases, and a third refloating
stage in the event of dismantling or repositioning of the
foundation system by evacuating the water ballast from the
previously ballasted cell groups to achieve positive buoyancy of
the foundation system.
19. The method of claim 18 wherein before the first transport stage
there are a series of foundation system manufacturing stages
comprising: a stage for the manufacturing of the floating concrete
bases at a dock of a port using a floating dock in which a steel
tubular projection is left embedded to serve as the connection
between the metal structure and the concrete bases, a stage for the
manufacturing of the metal structure on land, a stage for the
manufacturing of a connecting element that is the base of the wind
turbine, a stage of joining together the metal structure and the
floating concrete bases and of welding the connecting element to
the metal structure, and a stage for mounting the wind turbine onto
the connector element.
Description
OBJECT OF THE INVENTION
[0001] The present invention can be included in the technical field
of gravity-based foundation systems for the installation of
offshore wind turbines.
[0002] The object of the invention is a gravity-based foundation
system for the installation of offshore wind turbines which enables
the transporting, anchoring and subsequent refloating of the wind
turbine structure assembly once anchored, giving great versatility
to the solution with regard to the uncertainties associated with
the installation and how the terrain responds in the short and long
term, as well as the method for installing the preceding
gravity-based foundation system.
BACKGROUND OF THE INVENTION
[0003] One of the main problems of the offshore wind sector is the
support structure that serves as the base of the wind turbine. This
sector has addressed the development of fixed and floating wind
turbines depending on the depth at which the wind turbine is to be
installed. The technical and economic feasibility of offshore wind
systems requires the optimization and development of these support
structures.
[0004] Depending on the manner in which the structure is supported
on the seabed there are two generic types of fixed structures,
namely, those resting on the seabed, which are called gravity-based
structures, and those buried in the ground. Gravity-based
foundations are the solution used when the seabed is not suitable
for drilling, using the own weight of the foundation and of its
possible ballasting to maintain the turbine stable and upright. In
general, the solutions that have been developed for gravity-based
foundations can be classified both conceptually and constructively
in the following manner:
[0005] Conical frustum-shaped gravity-based foundation, with
varying slenderness and inclination of the conical section.
[0006] Foundation composed of a broad base on which a slender shaft
is built. It is a similar solution to that used in bridge
piers.
[0007] These solutions may include steel flaps at the base to
confine the terrain to facilitate the piling using suction chambers
and/or to develop localized terrain improvements, depending on the
characteristics thereof.
[0008] Selection of offshore wind turbine foundations, both for
piling and gravity-based solutions, is conditioned by two dominant
factors: the geomorphologic nature of the seabed and the depth of
the potential site.
[0009] As the depth of 40-50 meters is approached, offshore wind
turbine installation encounters economic and technical difficulties
that limit the development of this sector and its profitability.
The dimensions of the foundations, construction and on-site
installation difficulties, the loads transmitted to the terrain and
the potential loss of verticality of the assembly restrict the
available sites where it is feasible to develop these solutions in
the coastal shelf.
[0010] In addition to the difficulties addressed, installing some
of the solutions developed to date require the use of specialized
maritime means, specifically designed for transport and on-site
installation. Currently the number of ships available with these
features is very limited and the cost of freight or its
implementation is very high.
[0011] Systems known in the prior art include the international
application WO2011147592 on an offshore platform foundation
structure used for tripod or metal jackets consisting of one or
more solid elements with a flap on which the foundation legs are
supported.
[0012] The preceding structure requires expensive maritime means
presenting large lifting capacity to accomplish placement;
furthermore, this structure is not self-floating and it is not
possible to transport the wind turbine on the said structure from
land to the installation location.
[0013] Furthermore, according to this solution, the metal structure
formed by the tripod or jackets reaches the seabed, which increases
the use of metal and consequently the cost of such a solution,
besides it having a limited stability in the event of horizontal
movement.
[0014] Also known is the European patent application EP2539219
relating to a device and method for transporting and installing a
gravity-based foundation offshore wind turbine. Said solution is
not self-floating, it is expensive and requires marine means with
high lifting capacity for its placing, thus not allowing the
transport of the wind turbine on its structure from land, therefore
requiring the incorporation of additional weight to the structure
to increase its stability once anchored, by means of aggregate or
concrete blocks; accordingly, it is not compatible with low-bearing
capacity terrain and offers limited stability against
overturning.
DESCRIPTION OF THE INVENTION
[0015] The solution proposed by the present invention is based on
the use of three hollow reinforced concrete bases incorporating a
valve system whereby water is filled into and emptied out of its
interior acting as ballast. A metal structure connects these three
concrete bases with a shaft or connecting element, which starts at
the centre of the structure and emerges over the water surface, and
to which the element connecting the wind turbine tower will be
connected and on which the docking area, stairs and maintenance
platform will be installed.
[0016] After transporting the structure to its installation site,
the concrete bases fill with water for ballasting and anchoring by
means of traditional systems. The ballast system design allows the
refloating of the structure once anchored, which gives the solution
great versatility with regard to the uncertainties associated with
on-site installation and terrain response in the short and long
term.
[0017] The three legs provide greater stability compared to
mono-block gravity-based foundations. In addition to its enhanced
behaviour in less competent terrain, it provides a better load
distribution and transmits less stress to the terrain. The metal
structure enables the reduction of the section of the structure,
minimizing the contact surface with the waves and therefore the
stresses transmitted by the flow-structure interaction and reducing
the total weight of the foundation, lowering the centre of gravity
thereof and thus improving its navigability.
[0018] The proposed foundation based on the three self-floating
concrete bases is entirely modular so it is feasible to manufacture
it in several production centres for subsequent assembly at the
port.
[0019] The proposed solution is self-floating so it can be towed to
its final location. The triangle configuration of the floats
provides great naval stability. In addition, this structure allows
for the assembly of the wind turbine at the port, thus speeding up
the pace of assembly since smaller operating windows are
needed.
[0020] Conventional tugs are used for its transport. Since no
specific ships are needed, it is much easier to have several units
allowing the simultaneous transport and installation of several
systems, reducing installation costs and times.
[0021] Connecting the metal structure to the three concrete bases
is performed by three mixed connecting nodes each of which
comprises a concrete core and prestressed system integrated
therein.
[0022] This mixed connecting node responds optimally to the
construction needs, since it can be used as a purely prefabricated
system, with an arrangement capable of handling the execution and
assembly tolerances required; otherwise, as a partly prefabricated
system, combining the factory manufacturing of the metal structure
with the concreting of all or part of the node at the port.
[0023] The metal structure which joins the three concrete bases to
the connecting element comprises three inclined diagonal rods whose
ends which connect to each mixed connecting node are conical
frustum-shaped which enables the appropriate adjustment of the
mechanical constraints.
[0024] In this regard, the solution of the mixed connecting node
with a concrete core and prestressing system integrated therein
makes the following possible:
[0025] Ensuring that the axial actions of the rods converging on
the mixed connecting node converge on a given point, minimizing
actions due to the eccentricities of the components making up the
metal structure-mixed connecting node-floating concrete base
assembly.
[0026] Minimizing the physical dimensions of the mixed connecting
node which, receiving the ends of the rods converging therein,
envelops the convergence point.
[0027] Minimizing bending stresses by embedding the rods in the
mixed connecting node.
[0028] Conducting a dominant use of the prestressing system to
achieve the required capacity of transfer of force in the mixed
connecting node to the floating concrete base.
[0029] Each of the three floating concrete bases comprises a lower
slab which is in contact with the ground once the system is
submerged, an upper slab and a perimeter wall. These elements are
reinforced with concrete interior walls, which in turn define
groups of interconnected cells.
[0030] The floating concrete bases are executed by continuous
sliding on a floating platform and comprise a control system to
carry out the ballasting by means of a valve assembly arranged on
said floating concrete bases to allow the filling of a first group
of cells which are filled with water and injecting compressed air
for emptying them.
[0031] The floating concrete bases may optionally have a second
group of cells not involved in flotation in order to access from
the upper slab the contact surface between the lower slab and the
terrain, and thus improve the terrain bearing capacity or the level
of embedment therein.
[0032] Floating concrete bases perform the following functions:
[0033] Serving as a foundation to the metal structure to which the
connecting element of the wind turbine is attached during the
transport, anchoring and service stage.
[0034] Increasing naval stability during the transport and
anchoring stages both to allow navigation in more energetic
climatic conditions compared to those tolerated by single-volume
solutions, and to improve safety in the anchoring or submerging
stage of the structure as a whole.
[0035] Providing the system with towing points for the purpose of
its towing during transport stage with the possibility of
installing floats.
[0036] Increasing stability to prevent overturning and sliding,
placing the masses away from the roll-over and rotation centre,
which favours increased inertia of the structure assembly,
displacing the mass centre near the bottom.
[0037] Minimizing static and dynamic loads transmitted to the
terrain by increasing the distribution of burden of own weight per
unit of surface area and by enhancing the existence of restoring
forces.
[0038] Allowing the load transmitted by each caisson to be
different from that of the others during the service stage by means
of differential ballasting level.
[0039] Limiting global and differential sites in the short and long
term.
[0040] Keeping the metal structure supporting height at the same
depth, wherein only the mainstay of the concrete floating base
varies.
[0041] Controlling the naval stability and buoyancy during the
implementation, transport, anchoring and service stages.
[0042] The metal structure performs the following functions:
[0043] Serving as a transition element between the floating
concrete bases and the wind turbine connecting element, reaching a
shelter height over the maximum level reached by the free surface
of the sea.
[0044] Preventing relative movement between the floating concrete
bases.
[0045] Limiting or reducing the interaction between the sea flow
and the structure, which becomes greater as one approaches the
surface.
[0046] Limiting the transmission of high-frequency dynamic loads
between floating concrete bases and the terrain.
[0047] The procedure for the installation of an offshore wind
turbine foundation comprises the following stages:
[0048] A first transport stage wherein the foundation system is
towed from a collecting and/or assembly dock to the final location
by using tug boats where the floating concrete bases are
anchored.
[0049] A second anchoring stage wherein the foundation system is
anchored until making contact with the seabed modifying the overall
buoyancy by the controlled ballasting of some groups of cells in
the floating concrete foundations with the operation of valves
located in said bases, and
[0050] A third refloating stage in the event of dismantling or
repositioning of the foundation system by evacuating the water
ballast from the previously ballasted cell groups to achieve
positive buoyancy of the foundation system.
[0051] Between the second and the third stage there is the service
stage or stage in which the wind turbine is operated.
[0052] The gravity-based foundation system for offshore wind
turbine installation further comprises a control system which in
turn comprises a sensing subsystem, an operational control
subsystem and a decision-making subsystem during the
transportation, anchoring, service and refloating stages, wherein
the operational control subsystem enables the coordination between
the sensing subsystems and the decision-making support
subsystem.
[0053] One of the possible foundation manufacturing methods, taking
into account the development of civil engineering construction
techniques is as follows: Being a mixed structure of concrete and
steel, the manufacturing processes for the concrete bases and the
metal structure are independent. Concrete bases are manufactured at
the dock of a port using a floating dock, called floating caisson,
fitted with a sliding formwork system similar to that used in the
construction of concrete caissons for port docks. This process
enables the construction of a concrete base with high internal void
ratio that ensures adequate buoyancy thereof. During the
manufacturing process a steel tubular projection is left embedded
to serve as the connection between the metal structure and concrete
bases. The metal structure is manufactured in stages on land; on
the one hand the metal structure that connects to the concrete
bases and on the other hand the shaft or connecting element which
serves as the base of the wind turbine. The metal structure is made
by welding the joints. After finishing the concrete bases, and
being sheltered within the port, the bases are positioned and the
metal structure is installed by using a crane. Once the metal
structure is integral to the bases the metal shaft or connecting
element in positioned and welded to the rest of the structure. At
this time, the element is ready for pre-anchoring in a protected
area before its final transport and installation in the offshore
wind park. The transport process is performed by means of tugs,
which will place the element in its final position and the latter
will be anchored using anchors and winches, which will fix the
position of the structure. By means of a valve system installed in
the concrete base, it will fill up with water, allowing its
controlled anchoring until its positioning on the seabed.
[0054] The industrial application of the present invention is based
on the fact that the offshore wind energy industry is one of the
sectors for which most development is predicted in the coming
years. Currently, most of the major electricity developers and
technologists are studying the best alternatives for the
installation of offshore wind turbines.
[0055] The proposed solution solves the foundation for the
installation of the turbines in most of the sites addressed,
enabling the installation of thousands of wind turbines.
Technologists and ancillary industry will adapt their processes to
the manufacture and supply of these foundations.
[0056] The metal structure is composed of tubes whose size is
smaller than that of the wind turbine shafts themselves (6-3
meters), with potential synergies with the wind industry
itself.
[0057] This solution is completely modular and thus supports
manufacturing strategies in different centres for subsequent
assembly at the port. This will minimize potential problems in the
supply of materials. The caissons themselves are of a size such
that they could also be manufactured in different centres and
thereafter be transported to the assembly port.
DESCRIPTION OF THE DRAWINGS
[0058] To complete the description being made and for a better
understanding of the characteristics of the invention, according to
a preferred practical embodiment thereof, a set of drawings is
attached as an integral part of the description, which by way of
example without limiting the scope of this invention, show the
following:
[0059] FIG. 1--Shows a perspective view of a first embodiment of
the gravity-based foundation system for offshore wind turbine
installation of the present invention.
[0060] FIG. 2.--Shows an elevation view of FIG. 1.
[0061] FIG. 3.--Shows a plan view of FIG. 1.
[0062] FIG. 4.--Shows a perspective view of a second embodiment of
the gravity-based foundation system for offshore wind turbine
installation of the present invention.
[0063] FIG. 5.--Shows an elevation view of FIG. 4.
[0064] FIG. 6.--Shows a plan view of FIG. 4.
[0065] FIG. 7.--Shows a perspective view of a first embodiment of
the mixed connecting node between the metal structure and each of
the floating concrete bases.
[0066] FIG. 8--shows a plan view of the detail of the metal
structure rod connection to the mixed connecting node.
[0067] FIG. 9.--Shows a sectional view AA of FIG. 8.
[0068] FIG. 10.--Shows a sectional view BB of FIG. 8.
[0069] FIG. 11.--Shows a plan view of the detail of the metal
structure rod connection to the mixed connecting node according to
a second embodiment thereof.
[0070] FIG. 12.--Shows a sectional view AA of FIG. 11.
[0071] FIG. 13.--Shows a block diagram of the control system of the
gravity-based foundation system for offshore wind turbine
installation.
PREFERRED EMBODIMENT OF THE INVENTION
[0072] FIGS. 1 to 3 identify the main parts comprised by the
gravity-based foundation system for offshore wind turbine
installation according to a first embodiment. These figures
identify the following elements:
[0073] Floating concrete bases (1) or hollow concrete supports,
known as "caissons" in the field of maritime civil engineering,
with an integrated valve system to allow the ballasting and
de-ballasting of the base with water.
[0074] Tripod-shaped metal structure (2) attaching the concrete
bases to a connecting element (3) to the height of the wind turbine
installation.
[0075] Connecting element (3) between the floating concrete bases
(1, 4) and the wind turbine. It includes a maintenance ship docking
system and the stairs for access to the base of the wind turbine,
as well as the system for attaching the wind turbine to the
foundation.
[0076] FIGS. 4 to 6 show the main parts are identified comprised by
the gravity-based foundation system for offshore wind turbine
installation according to a second embodiment. These figures
identify the following elements:
[0077] Hollow reinforced floating concrete bases (4), known as
"caissons" in the field of maritime civil engineering, with an
integrated valve system to allow the ballasting and de-ballasting
of the base with water.
[0078] Lattice-shaped metal structure (5) as to join the floating
concrete bases (4).
[0079] Connecting element (6) between the floating concrete bases
(1, 4) and the wind turbine. It includes the maintenance ship
docking system and the stairs for access to the base of the wind
turbine, as well as the system for attaching the wind turbine to
the foundation.
[0080] In either embodiment, the attachment of the metal structure
(2, 5) to the three floating concrete bases (1, 4) is performed by
means of mixed connecting nodes (7, 27), one for each floating
concrete base (1, 4), each of which comprises a concrete core (8)
and a prestressing system (9) integrated therein.
[0081] The metal structure (2, 5) attaching the three floating
concrete bases (1, 4) to the connecting element (3, 6) comprises
three inclined diagonal rods (10) whose ends (11) which connect to
each mixed connecting node (7, 27) are conical frustum-shaped which
enables the appropriate adjustment of the mechanical
constraints.
[0082] The mixed connecting node (7, 27) further comprises a sheet
metal coating (12) externally covering the concrete core (8), a
metal coating (12) whose primary function is to assist in the
transfer and resistance to the stresses caused by the forces
introduced by the inclined diagonal rods (10) in the mixed
connecting nodes (7, 27), although it also acts as a closure and
protection element for the concrete core (8) used, to promote
durability conditions thereof and, above all, of the working
conditions of the prestressing system (9) situated in the mixed
connecting node (7, 27) of the metal structure (2, 5) and the
floating concrete base (1, 4).
[0083] The mixed connecting node (7, 27) further comprises anchors
that are actively involved in the transmission of forces, while the
floating concrete base (1, 4) comprises passive anchors disposed in
its interior, either directly in an upper closing slab (13) or in
rigidity partition walls or interior walls situated under the mixed
connecting nodes (not shown).
[0084] On these anchors arranged on the upper closure slab (13) or
on the rigidity walls the upper closure slab (13) of the floating
concrete base (1, 4)--where partly prefabricated--is concreted,
whereby only some sheaths with tendons inside (not shown) remain
exempt, while in the case of prefabricated mixed connecting nodes
(7, 27), the latter together with some sheaths, tendons and passive
anchors will be placed in an approximate position during the
concreting of the floating concrete base (1, 4).
[0085] In a first embodiment of the mixed connecting node (7) shown
in FIGS. 7 to 10, the metal coating (12) of the mixed connecting
node (7) has a polyhedral-like geometric shape with an upper
prismatic-trapezoidal-shaped area (14) wherein one of the sides
(15), the one that receives an inclined diagonal rod, is in turn
inclined and perpendicular to the inclined diagonal rod, and a
lower irregular prismatic-hexagonal-shaped area (16), wherein two
of its vertical sides (17), which receive some first auxiliary rods
(18) linking together two adjacent mixed connecting nodes (7) of
each floating concrete base (1), are perpendicular to said first
auxiliary rods (18), wherein the sides (15, 17) at which the
inclined diagonal rod and the first auxiliary bars join are made of
sheet steel.
[0086] Furthermore, at the mixed connecting node (7), a vertical
side (19) of the lower irregular prismatic-hexagonal-shaped area
(16) which is situated between the two vertical sides (17) that
receive the first auxiliary rods (18), receives a second auxiliary
rod (20) joining the mixed connecting node (7) to the connecting
element (3).
[0087] Therefore, in this first embodiment of the mixed connecting
node (7), said mixed connecting core (7) receives, via the metal
coating (12) with a tubular-like geometric shape, the inclined
diagonal rod (10), the first auxiliary rods (18) linking together
two adjacent mixed connecting nodes (7) of each floating concrete
base (1) and the second auxiliary rod (20) joining the mixed
connecting node (7) to the connecting element (3).
[0088] Inside the mixed connecting node, that is, in the concrete
core (8), the active anchors comprising:
[0089] transfer sheets (21) of the four rods (10, 18, 20) which
penetrate the mixed connecting node (7), wherein two of them, the
inclined diagonal rod (10) and the second auxiliary bar (20) are
joined together by welding at the point of intersection of the axes
of all the rods (10, 18, 20),
[0090] transfer and connecting sheets (22) joining the first
auxiliary rods together,
[0091] Additionally, the prestressing system (9) is also located
inside the mixed connecting node (7),
[0092] Once the preceding system has been placed, either on the
prefabrication bench, or at the port if the mixed connecting node
(7) is constructed therein, the node will then be concreted,
preceded in the latter case by the concreting of a connection area
between the mixed connecting node (7) and the floating concrete
base (1), a connection area left as a control element with assembly
and execution tolerances.
[0093] The prestressing system (9) arranged inside the mixed
connecting node (7) that penetrates the floating concrete base (1)
is then prestressed, followed by the injection of the sheaths, and
lastly the placing and welding of the metal coating (12) of the
mixed connecting node (7) which encloses the concrete core (8).
[0094] In a second preferred embodiment of the mixed connecting
node (27), shown in FIGS. 11 and 12, the mixed connecting node (27)
has a metal coating (23) with a tubular-like geometrical shape
arranged around a concrete core (24), wherein the metal coating
(23) is a steel pipe section open at its upper end, to enable the
concreting and the placing of the other elements described in the
first embodiment of the mixed node (7).
[0095] The mixed connecting core (27) receives, via the metal
coating (23) with a tubular-like geometrical shape, the inclined
diagonal rod (10), the first auxiliary rods (18) linking together
the two adjacent mixed connecting nodes (27) of each floating
concrete base (1) and the second auxiliary rod (20) which connects
the mixed connecting node (27) to the connecting element (3).
[0096] Inside the mixed connecting node (27), that is, in the
concrete core (24) the transfer sheets (21) are situated, as well
as the transfer and connection sheets (22), the prestressing system
(9) and the passive anchors as described above.
[0097] The gravity-based foundation system for offshore wind
turbine installation further comprises a control system which in
turn comprises a sensing subsystem (30), an operational control
subsystem (31) and a decision-making subsystem (32) during the
transport, anchoring, service and refloating stages, wherein the
operative control subsystem enables the coordination between the
sensing subsystems and decision-making support subsystem.
[0098] The sensing subsystem (30) comprises filling level sensors
(33) for the filling of the first group of cells whose function is
to measure their ballasting level during the towing, anchoring and
refloating stages. They are preferably situated on the lower
slab.
[0099] The sensing subsystem (30) further comprises inertial
acceleration sensors (34) preferably placed on the upper slab of
the caisson, in the mixed connection nodes joining and in the
connection between the connecting element of the wind turbine and
the metal structure. Their function is to measure the accelerations
to avoid exceeding the possible thresholds set by the turbine
manufacturer during the towing and anchoring stages.
[0100] The sensing subsystem (30) further comprises Doppler
acoustic sensors (35) for measuring currents in the vicinity of the
structure and the distance to the seabed. Its function is to
monitor the hydrodynamics surrounding the structure and to control
the position of each caisson relative to the seabed in the
anchoring stage and to support the erosion evolution
characterization during the service stage. They are located at the
point where the lower slab and the perimeter wall meet.
[0101] The sensing subsystem (30) further comprises a gyro (36) to
monitor the roll and pitch of each of the floating concrete bases
(1, 4), which are preferably arranged in the centre of each
floating concrete base. Its function is to control the verticality
of the system during the towing and anchoring stages.
[0102] The sensing subsystem (30) further comprises relative and
absolute positioning sensors (37) to locate the system during
transport and for its dynamic positioning during the anchoring
stage. They are arranged on top of the metal structure.
[0103] The sensing subsystem (30) further comprises pressure
sensors (38) for the estimation of the actions resulting from the
interaction between the flow of the sea and the structure during
the service stage. They are preferably arranged embedded inside the
perimeter walls of floating concrete bases.
[0104] The sensing subsystem (30) further comprises deformation
sensors (39) that enable the estimation of the number and magnitude
of stress load cycles of the system due to its interaction with the
ocean flow and/or cyclic stresses transmitted by the wind turbine.
They are preferably arranged at the nodes of the metal structure
and at the transition point between the metal structure and the
floating concrete bases.
[0105] The decision-making support subsystem (32) comprises a
logical device (40) which is a first-level instrumental alarm to
generate warnings to prevent exceeding the thresholds registered by
the sensing subsystem, and a second-level prediction device (41)
based on a climate prediction system (42) and on the instrumental
historical records obtained by the different sensors (33, 34, 35,
36, 37, 38, 39), performing a real-time control (43) by the
operational control subsystem (31) and may be displayed on a
display device (44); an operational control subsystem (31) acting
on the control actuators (45) that perform the opening and/or
closing of the valves (46) for water filling and emptying and on a
system of anchors and winches (47), to fix the position of the
foundation system, generating response scenarios for the foundation
system in the short and long term.
* * * * *